Water flood is a standard technique used to increase oil recovery from hydrocarbon fields. In a typical application, a plurality of injection wells at spaced locations in an older, somewhat depleted oil field are used to enhance the production of oil from production wells also spaced about the field. Pressurized water flows from an injection well through the permeable formation toward the relatively low pressure production well, which recovers oil with some water as the water flows through the formation toward the producing well. Those skilled in the art have long appreciated that while water flowing through the formation inherently carries some oil to the recovery well, water also tends over time to flow along the same well-established flow channels, which decreases the efficiency of the oil recovery operation. As a result of water flowing along these established flow channels, the water thus tends to entrain a smaller proportion of oil, so that the "water cut" of the produced fluids eventually exceeds the cost of separating the produced oil/water mixture into an economic hydrocarbon-based product.
To improve the recovery of oil using water flooding techniques, those skilled in the art have recognized the benefit of blocking established water channels through the formation to force the injected water to find new channels and thereby entrain new oil which is recovered with the water. U.S. Pat. No. 4,194,563 discloses a technique for improving water flooding operations by injecting a course emulsion into flow channels in the formation, then washing the wellbore with alcohol to remove the emulsion formed adjacent the wellbore. U.S. Pat. No. 4,529,523 teaches a method of enhancing water flooding by using a hydroxyethyl cellulose to prevent fingering of water through existing flow channels in the formation. U.S. Pat. No. 4,903,768 teaches a technique for controlling the profile of an oil/water interface in a high permeability zone, with either water flooding or carbon dioxide stimulation being used as the driving process. A breakthrough is shut-in using a temperature activated mixture which forms a solid blocking gel.
Those skilled in the art of water flooding also appreciate that an oil/water emulsion may be used to plug or at least reduce flow in a highly porous zone, thereby preventing undesirable water fingering and improving the flow of hydrocarbons to a recovery well. U.S. Pat. No. 3,472,319 teaches a technique for mixing an oil-in-water emulsion with a minimum of shear energy. The mixture is injected into the formation as a low viscosity emulsion, so that the oil droplets swell in the formation to plug or partially plug existing water channels. U.S. Pat. No. 3,724,546 teaches using a blood/water mixture for a water flooding operation. While various products have been used for injection with the water to assist in the water flooding operation by blocking or partially blocking the established flow channels, cellulose is a preferred injection product for many water flooding applications. The use of cellulose as a mixing material with the injection water is according well known, as evidenced by U.S. Pat. Nos. 3,848,673, 4,321,968, 4,451,389, 4,627,494, 4,629,575, and 5,100,567. The concentration of cellulose which is injected with the water into the formation may be varied. By optimising the fluid injection rates, the recovery of hydrocarbons can be increased during the secondary or tertiary recovery processes. U.S. Pat. No. 4,374,544 and European Publication 48 342 disclose techniques for optimising injection rates while also preventing fracturing of the formation, which may reduce the effectiveness of the oil recovery process.
Those skilled in the art of secondary and tertiary recovery of oil have generally recognized the benefits of trailer mounted mixing and injection devices, such as those disclosed in an article entitled "Enhanced Recovery Requires Special Equipment", Oil and Gas Journal, Jul. 12, 1976, pp. 50-56. U.S. Pat. No. 4,448,535 discloses portable apparatus for blending sands and solid additives at selected rates for injection with water into a well. A dry chemical is preferably fed into a mixing tank adjacent a variable venture nozzle, where the water is at a low pressure and is in high shear. European Patent Application No. 91309842.2 teaches a technique for mixing a solid and a fluid continuously to facilitate a gravel packing operation. A solids hopper with an internal auger is used to monitor the solids flow rate, with liquid being directed into the mixing chamber around the periphery of the auger. U.S. Pat. No. 4,311,395 discloses a chassis arrangement for mounting equipment used in well servicing operations. U.S. Pat. No. 4,077,428 teaches a transportable water injection plant for a water flooding operation. U.S. Pat. No. 4,534,869 teaches a portable filtration system with a three stage filtering process useful for a fracking operation. U.S. Pat. No. 4,597,437 discloses a portable plumbing and production assembly for use in hydrocarbon operations.
U.S. Pat. No. 4,518,261 discloses a process for dissolving a polyacrylamide powder in an aqueous solution for enhanced oil recovery. In order to prevent moisture build up and caking of the powder, a nitrogen blanket may be used. Polymers mixed with injection water in a flooding process may be transported to a mixer with dry air, as disclosed in U.S. Pat. No. 4,014,527. Systems for controlling the injection of a gel-type fluid into a well are disclosed in U.S. Pat. Nos. 3,707,191, 4,265,266, and 4,953,618. Equipment for mixing a dry material with water are disclosed in U.S. Pat. Nos. 3,902,558, 4,357,953, 4,725,379, and 5,190,374.
Although a great deal of effort has thus been expended to improve the recovery of oil using water flooding techniques, further improvements in this technology and associated reductions in the cost of recovery operations are essential if partially depleted hydrocarbon fields are to supply an increasing role in meeting future oil needs. Huge quantities of proven low pressure oil reserves exist in many parts of the world, and versatile equipment and improved techniques are required to economically recover those reserves.
The disadvantages of the prior art are overcome by the present invention, and improved oil recovery equipment and techniques are hereinafter disclosed for more efficiently recovering oil from depleted fields.